Acidic interchange of siloxane bonds with silicon-bonded alkoxy and acyloxy bonds



3,322,722 Patented May 30, 1967 ACIDIC HNTERQHANGE F SILOXANE BONDS WITH SILECON-BQNDED ALKDXY AND AC- YLUXY BONDS Benjamin A. Eynon, Midiand, Mich, assignor to Dow Corning Corporation, Midland, Mich., a corporation of Michigan No Drawing. Filled Oct. 18, 1965, Ser. No. 497,531

11 Claims. (Ci. 260-465) This application relates to a new process for the synthesis of organopolysiloxanes which contain siliconbonded alkoxy or acyloxy groups.

The process, which is particularly useful in the preparation of room-temperature curing silicone gels and elastomers, comprises reacting at a temperature of 20 to 150 C., in the presence of avcatalyst selected from the group consisting of strong acids and acidic salts thereof, (a) a silicone reactant comprising at least one organesilicon compound, said silicone reactant containing (1) siloxane bonds and (2) bonds selected from the group consisting of siliconbonded lower alkoxy and silicon-bonded lower acyloXy, the other bonds in said silicone reactant consisting essentially of those selected from the group consisting of ESlH, Si-monovalent hydrocarbon, Si-monova'lent halohydrocarbon, Si-divalent hydrocarbon-Si, and Sidivalent halohydrocarbon-Si, whereby an exchange reaction occurs between said bonds (1) and (2).

The preferred reaction temperature is from 50 to 130 C.

A typical example of the above following reaction:

|| H+ onmsiosuomn snooomn II II (CHa)aSiO S1(O 0 CH3): (CHa)aS1O C CH3 process is shown by the If ingredient (a) is more than one silicone compound the individual compounds need not contain both s'iloxane and alkoxy oracyloxy bonds, as long as both bonds are present in ingredient (a). An example of this type-of situation is shown in the above chemical Equation 1.

By lower alkoxy is meant radicals such as methoxy, ethoxy, isopropoxy, and n-hexoxy. By lower acyloxyf is means radicals such as Ingredient (a) can also contain other radicalsas defined above: suitable inonovalent hydrocarbon radicals are alkyl and cycloalkyl radicals such as methyl, ethyl,

propyl, sec-hexyl, cyclohexyl, and octadecyl; aliphatically unsaturated radicals such as vinyl, allyl, cyclohexenyl, and

Z-butenyl; and aryl-containing radicals such as phenyl,

tolyl, xenyl, naphthyl, and Z-phenylpropyl. 5 Examples of monovalent halohydrocarbon radicals are haloalkyl and halocycloalkyl radicals such as 3,3,3-trifluoropropyl, 5-chlorohexyl, and dibromocyclopentyl; aliphatically unsaturated radicals such as 4-bromobutenyl- 2 and trifluorocyclohexenyl; and aryl-containing radicals such as chlorophenyl, dibromophenyl, a,a,a-trifluorotolyl, and iodoxenyl.

Examples of divalent hydrocarbon and halo-hydrocarbon radicals are methylene, hexamethylene,

phenylene, Xenylene, chlorophenylene, and tetrafiuorophenylene.

Examples of suitable ingredients (a) are, therefore:

(a) (b) CH3 Eli 0 CH; C Hz (CH30)3S1O SiO SKO CH3)3, CH3 4 C H3 10 and i C FaCHzCI-IaSi O C CH3) 3 2113 (a) can SlO (CmHagSfi )0 and CH CHSKO CC2H5)3, C2115 2 4 and (C3H70)2Si-OSi(() 03H' 2 CH3 C H:

G1 Cl Si O O O and Further examples of ingredient (a) are shown below,

Any strong acid or acidic salt of a strong acid can be used as a catalyst in the process of this invention. The term strong acid includes any acid having a dissociation constant for its most acidic hydrogen atom of no less than 0.05 in a 0.1 N water solution at 25 C. The term acidic salt of a strong acid is defined as any salt of one of the above-defined acids which has a pH of less than 7 when tested as a 0.11 N water. solution at 25 C. Those salts which are more strongly acidic tend to have more catalytic activity than those which are nearly neutral.

Examples of such acids are sulfuric, nitric, hydrochloric, picric, pyrophosphoric, chromic, toluenesulfonic, chloroplat-inic, and trichloroacetic acids. Also included in the term strong acid are those ion exchange resins which have strong acid anions adsorbed or attached thereon. Examples of these are the commercially available sulfonated ion exchange resins. Acid clays are generally catalysts for this process, but they frequently cause undesirable side reactions and give poor yields. For example sulfuric acid-washed montmorrillonite is an operative catalyst in this invention.

Examples of operative acidic salts ar zinc chloride, aluminum chloride, nickel sulfate, cobaltic nitrate, stannic chloride and ferric nitrate.

The amount of catalyst present is not critical although the rate of the reaction will be affected thereby. Generally, from 0.2 to 20 weight percent, based on the weight of-the reaction mixture, can be used.

Solvents and dispersing agents can be used in this reaction, although they ar frequently unnecessary. Water, as a rule, should be avoided, since both silicon-bonded alkoxy and acyloxy groups are hydrolyzable. Examples .of suitable solvents are dichlor-obenzene, biphenyl, dibutylether, dodecane, isoctane, perchloroethylene, benzene, and toluene.

The application also relates to the process of reacting at a temperature of 50 C. to 150 C. in the presence of a catalyst selected from the group consisting of strong acids and acidic salts thereof, from 40 to 45 mol percent of a cyclic polysiloxane of the formula (R SiO) where R is selected from the group consisting of monovalent hydrocarbon and halohydrocarbon radicals and n has a valu of 3 to 8 with from to 60 mol percent of an organosilicon compound of the average formula where R is selected from the group consisting of lower alkoxy radicals and lower acyloxy radicals, and m has an average value of 0 to 1.9, whereby a composition which is curable to a rubbery gel upon exposure to moisture is formed.

The materials produced by this process are generally of low viscosity, but they cure to elastomeric materials upon exposure to moisture, for example, the moisture of the air.

An idealized example of such a reaction is:

which compound is curable by hydrolysis of the acetoxy groups and subsequent condensation on exposure to moisture.

The following examples are illustrative only and should not be construed as limiting the invention, which is properly delineated in the appended claims.

Example 1 There was placed into each of three flasks the following: 30.4 g. of hexamethyldisiloxane, 27,7 g. of methyltriacetoxysilane, and the following weights of the following catalysts:

flask (a)-2.9 g. of a sulfonated divinylbenzene-crosslinked polystyrene ion exchange resin (Amberlyst 15) flask (b)0.58 g. of sulfuric acid flask (c)-0.58 g. of zinc chloride.

The mixture was heated at 100 C. for about 23 hours. The products were analyzed by gas-liquid chromatography. Flasks (a), (b) and (c), were found to have produced a moderate to high yield of materials such as trimethylacetoxysilane, 1,1,1,3 tetramethyldiacetoxydisiloxane, and 3-acetoxyheptamethyltrisiloxane.

Example 2 Example 3 To 30 g. of a mixture of dimethylcyclopolysiloxanes consisting primarily of the cyclic tetramer and pentamer there was added 1 g. of methyltriacetoxysilane and l g. of the sulfonated ion exchange resin of Example 1.

This mixture was heated for 36 hours at 100 C. to yield a thick fluid that cures on exposure to the air for 24 hours to a clear, tacky, snappy elastomer, indicating that an acetoxysiloxane exchange reaction had taken place.

Example 4 To 370 g. of a mixture of dimethylcyclopolysiloxanes consisting primarily of the cyclic tetramer and pentamer, there was added 58 g. of vinyldimethylmethoxysilane and 21 g. of the sulfonated ion exchange resin of Example 1.

This was heated at about C. for about 12 hours, and filtered. The product was distilled. A higher boiling fraction of the distillate contained $113 (EH3 Cn2=CHSlO SiO CH5 CH3 CH3 10-15 Example 5 To 216 g. of 2-ethylbutylorthosilicate there was added 148 g. of the dimethylcyclopolysiloxane mixture of Example 4 and 18 g. of the sulfonated ion exchange resin of Example 1.

This was heated for 24 hours at C. Upon analysis by gas-liquid chromatography, it was found that the 2 ethylbutylorthosilicate content of the reaction mixture had declined considerably, compared with the original content.

The product cured to a sticky gel on exposure to the atmosphere for a week, giving further evidence that an alkoxysiloxane exchange reaction had taken place.

Example 6 To 128 g. of [(CH SiO] Si there was added 69.3 g. of ethylorthosilicate and 19.7 g. of the sulfonated ion exchange resin of Example 1.

This was heated at 89 C. for 18 hours to yield the following, as determined by gas-liquid chromatography: trimethylethoxysilane, hexamethyldisiloxane, and

where x is 1, 2 and 3.

Example 7 To 50 g. of an equimolar mixture of hexamethyldisiloxane and ethylorthosilicate there was added 1.19 g. of oxalic acid.

This was heated at 70 C. for 48 hours to obtain a moderate yield of trimethylethoxysilane and (C H O SiOSi (CH 3 Example 8 The experiment of Example 7 was repeated, substituting 2.7 g. of heptafluorobutyric acid for the oxalic acid ingredient.

This was heated at 70 C. for 48 hours to obtain a low yield of the products of Example 7.

- Example 9 To 162 g. of hexamethyldisiloxane there was added 60 g. of dimethyldimethoxysilane and a small amount of toluene-sulfonic acid.

This was heated at 80 C. for 24 hours to obtain a moderate yield of trimethylmethoxysilane, pentamethylmethoxydisiloxane, and octamethyltrisiloxane.

Example 10 To 106.4 g. of

CH3 (CF3CHzCH2S i)20 JHa there was added 20.8 g. of ethylorthosilicate and 6.3 g. of the sulfonated ion exchange resin of Example 1.

This was heated at 53 to 69 C. for 24 hours to yield the following products, as identified by gas-liquid chromatography:

CH3 CH3 CF3CH2CH S lOC2H5 and (CFaCHzCHgAiOLSKO CzH5)4-x (EH3 lHa where x is 1 and 2.

Example 11 To 92 g. of

CH3 (C1CHzS i)2O there was added 20 g. of ethylorthosilicate and 5.6 g. of the sulfonated ion exchange resin of Example 1.

This was heated at 70 C. for 24 hours to yield chloromethyldimethylethoxysilane and where x is 1, 2 and 3.

Example 12 Equimolar amounts of n-propylorthosilicate and symtetramethyldisiloxane were heated at 82 C. for 24 hours in the presence of the sulfonated ion exchange resin of Example 1.

The following compounds were recovered, as determined by gas-liquid chromatography: dimethylhydrogenpropoxysilane and and 0.1 g. of cupric sulfate are heated at C. for 24 hours, the following products are recovered:

To 126 g. of a trimethylsiloxane-endblocked dimethyl-polysiloxane having a viscosity at 25 C. of 200 cs. there was added 21 g. of ethylorthosilicate and 9 g. of the sulfonated ion exchange resin of Example 1.

This was heated for about 60 hours at C. The product was mixed with a trace of dibutyltindiacetate and exposed to the air.

It cured to a greasy gel in one day, indicating that an alkoxy-siloxane exchange reaction had taken place.

Example 15 When 5 g. of

0 CH CH3 0 [I I CH COS|1 SIIOCCHQ CH CH and 5 g. of octamethylcyclotetrasiloxane are heated at C. in the presence of 0.5 g. of cobaltic chloride, a siloxane-acetoxyinterchange reaction occurs, producing a copolymer of dimethylsiloxane units and CH3 (1H3 aOe CH3 CH3 units which contains silicon-bonded acetoxy groups.

That which is claimed is:

1. The process of reacting at a temperature of 20 to 150 C., in the presence of a catalyst selected from the group consisting of strong acids having dissociation constants for their most acidic hydrogen atom of no less than 0.05 in a 0.1 N water solution at 25 C., and acidic salts thereof which have a pH of less than 7 when tested as a 0.1 N water solution at 25 C., a silicone reactant comprising at least one organosilicon compound, said silicone reactant containing (1) siloxane bonds and (2) bonds selected from the group consisting of silicon-bonded lower alkoxy and silicon-bonded lower acyloxy, the other bonds in said silicone reactant consisting essentially of those selected from the group consisting of ESlH, Si-monovalent hydrocarbon, Si-monovalent halohydrocarbon, Sidivalent hydrocarbon-Si, and Si-divalent halohydrocarbon-Si, whereby an exchange reaction occurs between said bonds (1) and (2).

2. The process of claim 1 where the catalyst is a sulfonated, crosslinked, polystyrene resin.

3. The process of claim 1 where the catalyst is sulfuric acid.

4. The process of claim 1 where the reaction temperature is from 50 to C.

5. The process of reacting at a temperature of 50 to C., in the presence of a catalyst selected from the group consisting of strong acids having dissociation constants for their most acidic hydrogen atom of no less than 0.05 in a 0.1 N water solution at 25 C., and acidic salts thereof which have a pH of less than 7 when tested 7 as a 0.1 N water solution at 25 C., from 40 to 95 mol percent of a cyclic polysiloxane of the formula (R SiO) where R is selected from the group consisting of monovalent hydrocarbon and halohydrocarbon radicals and n has a value of 3 to 8 with from 5 to 60 mol percent of organosilicon compound of the average formula where R' is selected from the group consisting of lower alkoxy radicals and lower acyloxy radicals, and m has an average value of O to 1.9, whereby a composition which is curable to a rubbery gel upon exposure to moisture is formed.

6. The process of claim 5 where R is methyl.

7. The process of claim 5 where R is acetoxy.

8. The process of claim 5 where R is methoxy.

9. The process of claim 5 where R is ethoxy.

10. The process of claim 5 Where the catalyst is a sulfonated, crosslinked polystyrene resin.

11. The process of claim 5 where the catalyst is sulfuric acid.

References Cited UNITED STATES PATENTS 2,430,032 11/1947 Scott 26046.5 2,437,204 3/1948 McGregor et a1 260-465 2,627,451 2/1953 Erickson et a1. 260448.8 2,637,719 5/1953 Dereich 260-46.5 2,909,549 10/1959 Bailey 26046.5 3,004,053 10/1961 Shiihara 260-448.8 3,037,052 5/1962 Botnick 260-485 3,186,967 6/1965 Nitzsche et a1. 260-46.5 3,192,241 6/1965 Roebuck 26046.5

DONALD E. CZAJA, Primary Examiner.

LEON I. BERCOVITZ, Examiner.

M. MARQUIS, Assistant Examiner. 

1. THE PROCESS OF REACTING AT A TEMPERATURE OF 20* TO 150*C., IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF STRONG ACIDS HAVING DISSOCIATION CONSTANTS FOR THEIR MOST ACIDIC HYDROGEN ATOM OF NO LESS THAN 0.05 IN A 0.1 N WATER SOLUTION AT 25*C., AND ACIDIC SALTS THEREOF WHICH HAVE A PH OF LESS THAN 7 WHEN TESTED AS A 0.1 N WATER SOLUTION AT 25*C., A SILICONE REACTANT COMPRISING AT LEAST ONE ORGANOSILICON COMPOUND, SAID SILICONE REACTANT CONTAINING (1) SILOXANE BONDS AND (2) BONDS SELECTED FROM THE GROUP CONSISTING OF SILICON-BONDED LOWER ALKOXY AND SILICON-BONDED LOWER ALKOXY, THE OTHER BONDS IN SAID SILICON REACTANT CONSISTING ESSENTIALLY OF THOSE SELECTED FROM THE GROUP CONSISTING OF $SIH, SI-MONOVALENT HYDROCARBON, SI-MONOVALENT HALOHYDROCARBON, SIDIVALENT HYDROCARBON-SI, AND SI-DIVALENT HALOHYDROCARBON-SI, WHEREBY AN EXCHANGE REACTION OCCURS BETWEEN SAID BONDS (1) AND (2).
 5. THE PROCESS OF REACTING AT A TEMPERATURE OF 50* TO 150*C., IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF STRONG ACIDS HAVING DISSOCIATION CONSTANTS FOR THEIR MOST ACIDIC HYDROGEN ATOM OF NO LESS THAN 0.05 IN A 0.1 N WATER SOLUTION AT 25*C., AND ACIDIC SALTS THEREOF WHICH HAVE A PH OF LESS THAN 7 WHEN TESTED AS A 0.1 N WATER SOLUTION AT 25*C., FROM 40 TO 95 MOL PERCENT OF A CYCLIC POLYSILOXANE OF THE FORMULA (R2SIO)N WHERE R IS SELECTED FROM THE GROUP CONSISTING OF MONOVALENT HYDROCARBON AND HALOHYDROCARBON RADICALS AND N HAS A VALUE OF 3 TO 8 WITH FROM 5 TO 60 MOL PERCENT OF ORGANOSILICON COMPOUND OF THE AVERAGE FORMULA 